As known, a dispensing head generally comprises an enclosure that delimits a pumping chamber, a piston sliding into the pumping chamber, a trigger, manually actuable for acting on the piston and causing the fluid dispensing from the pumping chamber and elastic return means, acting on the trigger for returning the head from the dispensing configuration to the stand-by configuration.
Several embodiments of elastic return means exist.
Some embodiments envisage a spring, generally helical and made of a metal material, seated within the dispensing chamber and acting on the piston.
On the other hand, more recent embodiments envisage an elastic element arranged outside the pumping chamber and often made of plastic material; such embodiments allow obtaining important advantages especially in the reduction of the times and methods of assembly of the dispensing head in production.
Some examples of embodiments are shown in documents U.S. Pat. No. 6,267,271, JP-10-235245, U.S. Pat. No. 7,175,056, JP-09-253540, JP-09-314001, JP-10-128184 and U.S. Pat. No. 5,706,984.
However, known solutions comprise elastic elements that in the fluid dispensing step, that is, in the switching of the head from the stand-by configuration to that of dispensing, and vice versa, are subject to intense bending stresses.
Such elastic elements have shown poor reliability during the endurance tests performed, since notches into their structure and breakage occurred after running even a low number of cycles.